Common sense epidemiology: self-based judgments from laypersons and physicians.

This article reports two studies on a neglected aspect of common sense epidemiology: subjective estimates of the prevalence of symptoms and diseases. Based on social-psychological research on the false-consensus effect, it was hypothesized that subjects who had a history of a condition would estimate its prevalence to be greater than would subjects who did not have a history of that condition. This hypothesis was supported across several different symptoms and diseases. Expertise did not confer protection from the effect. It occurred among 110 college students in Study 1 as well as among 65 practicing physicians in Study 2. In addition, college students who estimated the prevalence of a condition as relatively high rated that condition as less life-threatening than did other students, and students who had a history of a condition rated it as less life-threatening than did their counterparts without such a history. The discussion focuses on (a) explanations of differences in prevalence estimates as a function of personal health history, (b) implications for laypersons' judgments of seriousness, their emotional reactions to illness threats, and their illness behavior, and (c) implications for physicians' diagnostic behavior.